The hormone oxytocin is potent contractor of the uterus and is used for the induction or augmentation of labour. Also the density of uterine oxytocin receptors increases significantly by >100 fold during pregnancy and peaks in labour (pre-term and term).
Pre-term births/labour (between 24 and 37 weeks) causes about 60% of infant mortality/morbidity and thus a compound which inhibits the uterine actions of oxytocin e.g. oxytocin antagonists, should be useful for the prevention or control of pre-term labour.
International patent application PCT/EP02/14823 describes a class of diketopiperazine derivatives which exhibit a particularly useful level of activity as selective antagonists at the oxytocin receptor. A preferred class of compounds described therein is represented by the formula A
Such compounds include those wherein inter alia R1 is 2-indanyl, R2 is C3-4alkyl, R3 is a 5 or 6 membered heteroaryl group linked to the rest of the molecule via a carbon atom in the ring, R4 represents the group NR5R6 wherein R5 and R6 each represent alkyl e.g. methyl or R5 and R6 together with the nitrogen atom to which they are attached form a 3 to 7 membered saturated heterocyclic ring which heterocycle may contain an additional heteroatom selected from oxygen.